This invention relates to cling film having a controlled topographical surface of microchannels and the methods of making and using them.
Cling film, also known as static cling film, is applied to windows and smooth surfaces for temporary use as signage or other functional applications such as sun shade films. The natural adhesion of the smooth flexible film can provide sufficient holding power while still allowing easy removal. During application, the contact of the film surface with substrate results in instantaneous adhesion. Attempts to achieve uniform contact over the entire smooth surface often result in entrapment of air bubbles and large air pockets, which are not easily pressed out.
Anyone who has ever attempted to hang wallpaper can appreciate the frustration that can arise when entrapped air beneath a film can not be removed easily. The most common solutions to this problem are to remove and reapply the film or to perforate the film to release the entrapped air. Multiple attempts to adhere the same film to a substrate can compromise its appearance or increase the probability of uneven or misaligned film on the substrate. Perforating a film mars its appearance. The removal of air bubbles is also labor intensive.
For cling films, prior common solutions to this problem are to remove and reapply the film, which can contaminate the film. Any attempt to press out some of the air bubbles usually has limited effectiveness. Another solution to the problem is to wet the substrate or the film before application, which tends to cause the film to slide on vertical surfaces even if the messiness of the application is deemed acceptable. One might think that a substrate can be textured to permit egress of fluids during film application, but that textured surface may not have enough contact area for the cling film to cling for the desired period of time. So, there are no good solutions to this problem in the art.
The problems in the art of cling film construction and application are solved by the present invention through the addition of an engineered topography to one major surface of the film.
Desirably, the addition of topography to a surface of cling film should take the following factors into consideration:
(1) A cling film without channels provides no effective route for egress of fluids in the X-Y dimensions of the interface between the film and the substrate, especially if the film is fluid-impermeable. But if the channels are too large, a path of fluid egress could also be a path of passive ingress of the same or other fluids.
(2) The film, and especially its outer imagable surface, can not be adversely affected by the topography chosen, thereby limiting the size of the channels in the film and also limiting the method of construction. The film needs at least one flat, uniform surface for imaging and other aesthetic reasons. The formation of large channels into the opposing major surface of the film will adversely disrupt the flat, uniform surface of the film used for imaging. Also, topographies that are too large will create undesired undulations or other imperfections in the appearance of the film on the final substrate. Such undulations or other imperfections make the image graphic unacceptable for most commercial markets, even in the inexpensive cling film market.
(3) The area of cling film actually contacting the substrate and the holding power (e.g., shear and peel clinging) of the cling film affect bonding performance of the film to the substrate. If either the holding power is too weak or the area of the film contact is too small, or both, the performance of the cling film to adhere without the use of adhesive is entirely inadequate. Where there is film contact with the substrate, the nature of contact should be substantially flat.
While the air bubble and fluid egress problems associated with large format graphics are easy to understand, these problems also exist for small graphics and decals where speed of application are significant for economic or manufacturing considerations.
The problem of fluid egress is even more acute whenever the film effectively inhibits any egress in the Z axis.
The art clearly needs a different approach to make cling film easy, fast, and uniform to apply to substrates in a manner that controls fluid egress within the three enumerated factors stated above. Indeed, the art needs to engineer the geometry of the film surface to provide a controlled topography at any film-substrate interface where particular performance is required. Moreover, the art needs to make a cling film that controls fluid egress without harming the essential performance of the film clinging to the substrate for the desired period of time.
The present invention solves the problem of entrapped air between cling film and a substrate such as glass by incorporating micro-channeled topography on the mounting surface of the cling film. The topography can be imparted during manufacture by known embossing, casting, or coating microreplication methods. When the relatively planar cling surface is contacted to the substrate, the small channels allow the egress of air or other fluid. Moreover, the small channels do not adversely affect the essential performance of the film to cling to the substrate.
Preferably, the pattern chosen for creating the microchannels can be square, diamond, hexagonal, or parallel with shapes being any of rounded, triangular, trapezoidal, or rectangular. Sizes of the pattern depends on the thickness of the cling film and can be as small as less about 0.1 mm wide and less than 25 xcexcm deep to offer flexible performance design. The total area of microchannels can be controlled such that a substantial portion of the cling vinyl would remain relatively unchanged to provide sufficient bonding surface.
For this invention, that particular performance should include the provision for fluid egress in the X-Y dimensions of the film-substrate interface but without adversely affecting the desired appearance of the outer imageable surface which should remain flat and uniform for imaging. Further, fluid egress should be balanced against xe2x80x9cclingingxe2x80x9d bond strength for maintaining the interface, i.e., assuring the film will continue to cling to the glass.
One aspect of the present invention provides a means of controlling the topography of a cling film surface, comprising contacting a microembossed pattern to a major surface of the cling film and forming a microreplicated surface, such that when an interface is established between the film and a supporting substrate, the topography of the film surface controls the performance of the interface between that film and the supporting substrate.
xe2x80x9cCling filmxe2x80x9d means any form of polymeric film that has sufficient properties on at least one major surface thereof, at the time of application to a supporting substrate, to cling by application of static interaction to that substrate without the application of an adhesive between the film and the substrate.
Another aspect of the present invention provides a microreplicated film surface formed by microreplication from any contacting technique such as casting, coating, or compressing techniques. Microreplication can be achieved by at least any of (1) casting or extruding using a tool having a microembossed pattern, (2) coating of a film onto a release linear having that microembossed pattern, or (3) passing through a nip roll to compress the film against a release liner having that microembossed pattern. Desired embossing topography can be formed in tools via any of a number of well-known techniques, selected depending in part upon the tool material and features of the desired topography. Illustrative techniques include etching (e.g., via chemical etching, mechanical etching, or other ablative means such as laser ablation or reactive ion etching, etc.), photolithography, stereolithography, micromachining, knurling (e.g., cutting knurling or acid enhanced knurling), scoring or cutting, etc.
The microreplicated topography resides on at least one major surface of the film and can optionally reside on both major, opposing surfaces of the film affecting the properties of the interface(s) in the same or different manners, as desired by those skilled in the art.
When a microembossed liner is used, the liner can be a release liner (e.g., a releasable storage liner for the adhesive or a transfer liner for moving the film from one location to another) or a tape backing on a self-wound roll that also serves as a liner, such that the microembossed surface of the tape backing microreplicates the surface of the film exposed as the tape is unwound.
xe2x80x9cMicroembossedxe2x80x9d means a topography on the liner or the casting tooling having an effective three-dimensional pattern that generates a depth less than the thickness of the continuous film. The pattern can be interconnected or continuously parallel.
xe2x80x9cInterconnectedxe2x80x9d means that at least two three-dimensional features in the microembossed pattern intersect causing the microreplicated formation of an intersection of the inverse of such three-dimensional features in the film surface.
xe2x80x9cMicroreplicated filmxe2x80x9d means film having a topography in at least one major, substantially continuous surface that is essentially, but not necessarily perfectly, the inverse of the microembossed pattern to which the film surface is contacted and has a contact area of at least about 35%.
xe2x80x9cPatternxe2x80x9d means any formation of embossings that can utilize any theory of geometry, including without limitation, Euclidian geometry and fractal geometry.
Optionally, the microembossed patterns can be multiple. xe2x80x9cMultiplexe2x80x9d means two or more embossing patterns are superimposed on the tool or liner to create a complex pattern of differing depths or heights of embossing to form the microreplicated film having a complex pattern of differing depths or heights.
Another aspect of the present invention is an article having a microreplicated cling film of the present invention.
The microembossed liners, tools, or nip rolls used to make microreplicated film of the present invention can provide a vast array of microreplication combinations given the multitude of microembossed patterns, the multiplicity of embossings, and the variety of materials available.
A feature of microreplicated films of the present invention is that the microembossed pattern is retained for an effective period of time on the microreplicated film during intended use. The retention of microreplication can range from minutes to years depending upon the rheology of the film chosen and the conditions of application. Fluid egress may only be desired for limited times.
The invention not only provides a three-dimensional topography for films, but because of the unusual properties of cling vinyl materials, their flow characteristics can be engineered. Therefore, the invention also contemplates the effective use of the polymer chemistry and substrate application techniques to control the fourth dimension, how long after substrate application the surface of the film remains three-dimensional. The topography need not be permanent. For example, it can be desired to collapse any portion of the film-substrate interface after sufficient fluid egress is completed.
Another feature of the microreplicated adhesive topography is the ability to control the engineering of the interface for desired uses, such as air bleeding from large image graphics, plasticizer migration routes from plastic materials, and other applications that require fluid transport in the X-Y dimensions of the interface(s) rather than the Z axis from the surface of the adhesive. In other words, aerodynamics of the film interface can be engineered as required.
An optional feature of the microreplicated film, when using multiple microembossed patterns, is the ability to control the types of materials introduced into recesses of differing depths in the topography for complex film usages, such as positionability of adhesives as that disclosed in U.S. Pat. Nos. 5,296,277 and 5,362,516 (both Wilson et al.) and U.S. Pat. No. 5,141,790 (Calhoun et al.) and U.S. patent application Ser. No. 08/559,037 (Keller et al.) filed Nov. 15, 1995, the disclosures of which are incorporated by reference therein.
An advantage of the present invention is the creation of an engineered cling film surface that serves specific intended uses for a controlled period of time when transferred or adhered to another material.
Another advantage of the present invention is a cling film that provides effective fluid egress without adversely affecting its appearance when clinging onto the substrate.
Another advantage of the present invention is the ability of the film surface(s) to exhaust fluids such as gases, entrapped air, plasticizers, or moisture from the plane of the adhesive surface independent of specialized compositions or formulations of the film.
Another advantage of the present invention is the formation of the same or different adhesive topographies to each of the opposing major surfaces of the film for performance and decorative reasons, or both. For example, one film interface could provide plasticizer migration from one engineered topography and the opposing major surface could provide fluid egress from a second engineered topography.
Another advantage of the present invention is the ability of the film surface(s) to permit controlled ingress of fluids at a desired time to affect the interface(s), such as to facilitate removal, alter surface characteristics, provide additional remedial treatments, and the like.
Other features and advantages will become apparent from the embodiments of the invention described below in relation to the Figure.